[libvirt] [PATCH] conf: Add check to avoid a NULL compare forSysfsPath

[cheng.lin130 at zte.com.cn]

> On 01/18/2019 02:49 AM, Cheng Lin wrote:
> > If the two sysfs_path are both NULL, there may be an incorrect
> > object returned for virNodeDeviceObjListFindBySysfsPath().
> >
> > This check exists in old interface virNodeDeviceFindBySysfsPath().
> > e.g.
> > virNodeDeviceFindBySysfsPath(virNodeDeviceObjListPtr devs,
> >                              const char *sysfs_path)
> > {
> >     ...
> >         if ((devs->objs[i]->def->sysfs_path != NULL) &&
> >             (STREQ(devs->objs[i]->def->sysfs_path, sysfs_path))) {
> >     ...
> > }
> >
> > Signed-off-by: Cheng Lin <cheng.lin130 at zte.com.cn>
> > ---
> >  src/conf/virnodedeviceobj.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/src/conf/virnodedeviceobj.c b/src/conf/virnodedeviceobj.c
> > index c8ad131..2e40de5 100644
> > --- a/src/conf/virnodedeviceobj.c
> > +++ b/src/conf/virnodedeviceobj.c
> > @@ -207,7 +207,8 @@ virNodeDeviceObjListFindBySysfsPathCallback(const void *payload,
> >      int want = 0;
> >
> >      virObjectLock(obj);
> -    if (STREQ_NULLABLE(obj->def->sysfs_path, sysfs_path))
> > +    if ((obj->def->sysfs_path != NULL) &&
> > +        (STREQ_NULLABLE(obj->def->sysfs_path, sysfs_path)))
> >          want = 1;
> >      virObjectUnlock(obj);
> >      return want;
> >
> 
> Thanks, I reformatted to this and pushed:
> 
> @@ -207,7 +207,8 @@ virNodeDeviceObjListFindBySysfsPathCallback(const
> void *payload,
> int want = 0;
> 
> virObjectLock(obj);
> -    if (STREQ_NULLABLE(obj->def->sysfs_path, sysfs_path))
> +    if (obj->def->sysfs_path &&
> +        STREQ_NULLABLE(obj->def->sysfs_path, sysfs_path))
> want = 1;
> virObjectUnlock(obj);
> return want;
> 
> What kind of devices are you seeing that don't have a sysfs_path I?
> Seems like there's lots of places internally we expect it to be there,
> but some others where we don't, so people must have hit similar issues
> before, but I don't think I see an example in the udev output on my machine

The new interface handles null parameters differently from the old one. 
Potential risks may be introduced.

> - Cole